Constitutive Neutrophil Apoptosis: Regulation by Cell Concentration via S100 A8/9 and the MEK – ERK Pathway

Abstract

Programmed cell death (PCD) is a fundamental mechanism in tissue and cell homeostasis. It was long suggested that apoptosis regulates the cell number in diverse cell populations; however no clear mechanism was shown. Neutrophils are the short-lived, first-line defense of innate immunity, with an estimated t = 1/2 of 8 hours and a high turnover rate. Here we first show that spontaneous neutrophil constitutive PCD is regulated by cell concentrations. Using a proteomic approach, we identified the S100 A8/9 complex, which constitutes roughly 40% of cytosolic protein in neutrophils, as mediating this effect. We further demonstrate that it regulates cell survival via a signaling mechanism involving MEK-ERK via TLR4 and CD11B/CD18. This mechanism is suggested to have a fine-tuning role in regulating the neutrophil number in bone marrow, peripheral blood, and inflammatory sites.

Neutrophil transcriptional profile changes during transit from bone marrow to sites of inflammation

“…4,10,29,30 The Bcl-2 family, which we observed in our microarray analysis to be differentially expressed between compartments, is an important regulator of neutrophil apoptosis. 5,31 Here we found a mixed pattern with both pro-apoptosis and pro-survival genes with altered regulation, as neutrophils leave the circulation and arrive at the site of inflammation with downregulation of FasL, CR3 (Mac-1), caspase 2 and 9 and upregulation of Fas, Daxx, cIAP and NfkB. Additionally, members of the TLR family including TLR2 and TLR4 were decreased in PMN-PE (Figure 4a and b and Supplementary Table 13).…”

The Thr224Asn mutation in the VPS45 gene is associated with the congenital neutropenia and primary myelofibrosis of infancy

“…Blood neutrophils were isolated from fresh blood samples obtained from the patients as described in Atallah et al 9 Constitutive apoptosis was induced by resuspending neutrophils with cell culture medium and 10% of autologous plasma. Cells were cultured in 24-well plates at 37°C for 4 hours in a humidified incubator containing 5% carbon dioxide.…”

“…We also compared spontaneous constitutive neutrophil apoptosis 9 following 4 hours of in vitro incubation, in order to observe apoptosis progression. As shown in Figure 6C (right), the baseline MF of neutrophil annexin V staining was 145 compared with 51 of the control (P , .0001), and 4 hours later, it was 274, whereas in the control it raised only to an MF of 72 (P , .004) ( Figure 6B).…”

Apoptotic activity of isoespintanol derivatives in human polymorphonuclear cells

“…Various signaling pathways confer these features. Each pathway is responsive to specific endogenous stimuli and mediates pro-or anti-apoptotic effects; some are dependent on the intervention of caspases and other independents (1,(13)(14)(15)(16)(17).…”